Public bug reported:
We are seeing a reproducible IPv6 regression on Ubuntu guests running on
Microsoft Hyper-V.
After booting a newer kernel, same-subnet IPv6 connectivity still works
and the configured IPv6 default gateway remains reachable, but routed
IPv6 traffic to external networks stops working.
Observed behavior on the affected kernel:
Static IPv6 address is configured correctly.
IPv6 default route is present.
Neighbor discovery for the default gateway succeeds.
Same-subnet IPv6 communication works.
Outbound TCP SYN packets are visible leaving eth0.
No TCP SYN-ACK replies are received for routed IPv6 destinations.
Connections such as curl -6 https://google.com/ time out.
The issue is reproducible by changing only the running kernel.
Confirmed on Ubuntu 24.04.5 LTS:
6.8.0-146-generic: routed IPv6 is broken
6.8.0-124-generic: routed IPv6 works
After booting 6.8.0-124-generic on the same VM, without changing the
network configuration, routed IPv6 immediately works again.
Example after booting the working kernel:
$ uname -r
6.8.0-124-generic
$ curl -6 -v --connect-timeout 5 https://google.com/
* IPv6: 2a00:1450:400e:806::200e
* Trying [2a00:1450:400e:806::200e]:443...
* Connected to google.com (2a00:1450:400e:806::200e) port 443
...
< HTTP/2 301
The same type of issue was also observed on other Ubuntu Hyper-V guests
after rebooting into a newer kernel version, while older kernels
continued to provide working routed IPv6 connectivity.
Environment:
Microsoft Hyper-V
Ubuntu virtual machines
hv_netvsc network driver
Static IPv6 configuration
IPv6 gateway remains reachable while external/routed IPv6 fails
Problem appears only after booting the newer kernel
Rolling back to the previous kernel restores IPv6 connectivity
This appears to be a kernel regression affecting IPv6 networking on
Hyper-V, potentially involving hv_netvsc, offloading, IPv6 routing, or
packet handling in the networking stack.
AI was involved trouble shooting + writing report.
ProblemType: Bug
DistroRelease: Ubuntu 24.04
Package: linux-image-6.8.0-124-generic 6.8.0-124.124
ProcVersionSignature: Ubuntu 6.8.0-124.124-generic 6.8.12
Uname: Linux 6.8.0-124-generic x86_64
AlsaDevices:
total 0
crw-rw---- 1 root audio 116, 1 Oct 5 14:14 seq
crw-rw---- 1 root audio 116, 33 Oct 5 14:14 timer
AplayDevices: Error: [Errno 2] No such file or directory: 'aplay'
ApportVersion: 2.28.3-0ubuntu0.1
Architecture: amd64
ArecordDevices: Error: [Errno 2] No such file or directory: 'arecord'
AudioDevicesInUse: Error: command ['fuser', '-v', '/dev/snd/seq',
'/dev/snd/timer'] failed with exit code 1:
CRDA: N/A
CasperMD5CheckResult: pass
CloudArchitecture: x86_64
CloudID: none
CloudName: none
CloudPlatform: none
CloudSubPlatform: config
Date: Mon Oct 5 14:16:34 2026
InstallationDate: Installed on 2025-02-24 (588 days ago)
InstallationMedia: Ubuntu-Server 22.04.2 LTS "Jammy Jellyfish" - Release amd64
(20230217.1)
IwConfig: Error: [Errno 2] No such file or directory: 'iwconfig'
Lspci:
Lspci-vt:
Lsusb: Error: command ['lsusb'] failed with exit code 1:
Lsusb-t:
Lsusb-v: Error: command ['lsusb', '-v'] failed with exit code 1:
MachineType: Microsoft Corporation Virtual Machine
PciMultimedia:
ProcEnviron:
LANG=en_US.UTF-8
PATH=(custom, no user)
SHELL=/bin/bash
TERM=xterm-256color
ProcFB: 0 hyperv_drmdrmfb
ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-6.8.0-124-generic
root=UUID=98ca6a83-c6c3-4b3b-9008-0b5aa7d3658b ro
RelatedPackageVersions:
linux-restricted-modules-6.8.0-124-generic N/A
linux-backports-modules-6.8.0-124-generic N/A
linux-firmware 20240318.git3b128b60.0ubuntu3.1
RfKill: Error: [Errno 2] No such file or directory: 'rfkill'
SourcePackage: linux
UpgradeStatus: Upgraded to noble on 2025-10-16 (354 days ago)
dmi.bios.date: 10/24/2025
dmi.bios.release: 4.1
dmi.bios.vendor: Microsoft Corporation
dmi.bios.version: Hyper-V UEFI Release v4.1
dmi.board.asset.tag: None
dmi.board.name: Virtual Machine
dmi.board.vendor: Microsoft Corporation
dmi.board.version: Hyper-V UEFI Release v4.1
dmi.chassis.asset.tag: 9951-8663-8474-8683-4797-8379-38
dmi.chassis.type: 3
dmi.chassis.vendor: Microsoft Corporation
dmi.chassis.version: Hyper-V UEFI Release v4.1
dmi.modalias:
dmi:bvnMicrosoftCorporation:bvrHyper-VUEFIReleasev4.1:bd10/24/2025:br4.1:svnMicrosoftCorporation:pnVirtualMachine:pvrHyper-VUEFIReleasev4.1:rvnMicrosoftCorporation:rnVirtualMachine:rvrHyper-VUEFIReleasev4.1:cvnMicrosoftCorporation:ct3:cvrHyper-VUEFIReleasev4.1:skuNone:
dmi.product.family: Virtual Machine
dmi.product.name: Virtual Machine
dmi.product.sku: None
dmi.product.version: Hyper-V UEFI Release v4.1
dmi.sys.vendor: Microsoft Corporation
** Affects: linux (Ubuntu)
Importance: Undecided
Status: New
** Tags: amd64 apport-bug noble
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https://bugs.launchpad.net/bugs/2169580
Title:
IPv6 routed connectivity broken on Hyper-V after kernel update; works
again with previous kernel
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